This invention relates to maintenance and service of complex systems and more specifically methods and apparatus for improving fault isolation for such systems.
Complex systems comprising tens or hundreds of inter-related and inter-operating systems and subsystems, many which may be complex in their own right, present unique maintenance and service challenges. Examples of such complex systems include factories, major buildings, ocean-going vessels, power generation plants, and aircraft to name a few. Complex systems and the inter-related and inter-operational nature of the systems and subsystems thereof often require equally complex and disciplined maintenance and service programs. These programs usually include documentation or records of observed or indicated irregularities or discrepancies and actions taken or services performed pursuant to resolution or prevention of such irregularities and discrepancies. This documentation is usually filled out, completed, or recorded by service and maintenance personnel. Expert systems and tools that can standardize service and maintenance documentation, diagnoses, procedures, cost estimates and so on are highly desirable for the time savings and precision they can offer to an overall maintenance and operational support program.
In the aircraft industry, for example, fault models that include inter alia fault codes as a means to summarize the set of symptoms or standard observations that are expected to be present for each distinct fault condition in a particular type of aircraft have more recently been used. A fault code typically corresponds to a fault condition in a single system on the aircraft and is often used as the basis of diagnostic endeavors, including fault classification and fault isolation, material planning, cost estimation, and deferral/criticality analysis. Thus Fault Codes are a critical element of the Fault Model for an aircraft where a model is used to support an automated diagnostic and maintenance support system. Equally critical therefore is determining the proper fault code for the aircraft when presented with a discrepancy and set of symptoms or a given fault condition. Finding or determining or selecting the proper fault code based on readily apparent symptoms or observations is referred to as fault classification.
Given the fault code, using additional symptoms, only available as test results, to determine the best repair is called fault isolation. Presently airline personnel or technicians often perform the fault isolation activity using documented Fault Isolation Procedures or through their individual knowledge of the aircraft systems involved. Use of these Fault Isolation Procedures by themselves is inadequate because the complexity of the system allows for a much greater variety of failure modes than can be anticipated by the author of the Procedures document. Reliance on the expertise of the technician is inadequate since the technician may be called upon to service 100""s of different aircraft in a year, each of which are substantially different, such as a Boeing 757 and Airbus A320, or have significant variation, such as the differences between the 757-27A and the 757-27B sub-fleets. A typical US airline will have several major fleets and a dozen or more sub-fleets. In addition, the configuration of the aircraft changes over time to incorporate safety, reliability and passenger comfort improvements. These changes are incorporated over a period of time thereby resulting in further ambiguity for the technician trying to analyze an aircraft fault condition without support.
Other systems for automated support of Fault Isolation such as those available from Boeing, often referred to as PMA in the industry and Airbus, typically referred to as CATS, help to identify the fault isolation diagram (tree) to use but do not provide a mechanism for incorporating experience into this decision or to effectively modify the decision tree itself based on this experience. Thus fault isolation remains a very time consuming and error prone activity that adds complexity to the diagnostic and service procedures, increases costs, and reduces the precision of planning and cost analysis activities. Clearly a need exists for methods and apparatus for improving fault isolation for complex systems, such as aircraft, preferably methods and apparatus that incorporate experience into such methods and apparatus.
The present invention in varying scope is a method and apparatus for improving fault isolation for failure modes in complex systems. One aspect of the invention is a software program comprising software instructions arranged to run on a processor to improve fault isolation for failure modes in a complex system, the software program when installed and operating on a processor resulting in the processor performing an inventive method of fault isolation. Another aspect according to the invention is a computer based aircraft maintenance and operations diagnostic system for improved assistance with fault isolation for a fault condition within an aircraft based on a fault model for the aircraft, the computer utilizing an inventive embodiment of a fault isolation software program to performs another inventive method of fault isolation.
In one aspect the method includes the steps of: capturing a set of symptoms that is consistent with a failure mode of the complex system; identifying a set of repairs for the complex system that are consistent with the set of symptoms; ranking, when the set of repairs includes more than one repair, the repairs in a sequence that will minimize an average cost to repair the complex system, the sequence including a historical component and reflecting the effectiveness of available test results to resolve each of said set of repairs; determining possible tests that are consistent with the failure mode; and ranking the possible tests according to there respective net improvement in the average cost to repair the complex system.
In narrower scope one aspect of the method includes selecting a test and obtaining a test result from the possible tests and repeating, using the set of symptoms, the test result, and any additional test results for tests that will be selected, the steps of identifying, ranking the set of repairs, determining the possible tests, ranking the possible tests and selecting further tests until the set includes only one repair and then reporting this repair. The process of capturing the set of symptoms, preferably, includes using a standard code as an indication of a set of standard observations corresponding to a subset of observable symptoms from the set of symptoms, the standard observations selected from a standard observations list and wherein the possible tests correspond to the standard code and wherein the step of identifying the set of the repairs includes identifying a list of repairs corresponding to the standard code for the set of symptoms. Preferably ranking the repairs further uses an assessment of experience with the set of symptoms occurring with each repair of the set of said repairs, whether the available test results indict, acquit, or are silent with respect to each repair, and a cost associated with each repair. Ranking the possible tests, preferably, uses an algorithm to rank the possible tests according to a value of the possible test that is dependent on a reduction in the average cost minus a cost to conduct the possible test.
The software program is particularly suitable for use within a diagnostic tool for application to complex systems. In one aspect, using an embodiment of the software program, the invention is an aircraft maintenance and operations diagnostic system for improved assistance with fault isolation for a fault condition within an aircraft based on a fault model for the aircraft, where the system comprises: a user interface; a computer, coupled to the user interface, having memory for storing software instructions and databases and a processor for; executing the software instructions to process information to facilitate the fault classification for the fault condition according to the fault model, the software instructions resulting in the computer: capturing a fault code from a fault classification process, the fault code being part of the fault model that is consistent with the fault condition; identifying a set of repairs for the complex system that are consistent with the fault code; ranking, when the set of repairs includes more than one repair, the repairs in a sequence that will minimize an average cost to repair the aircraft, the sequence including a historical component and reflecting the efficacy of available test results in resolving each repair; determining possible tests that are consistent with the fault code; and ranking the possible tests according to there respective net improvement in the average cost to repair the aircraft.
The above system in further inventive and narrower scope further includes a process of selecting a test and obtaining a test result from the possible tests and repeating, using the fault code, the test result, and any test results from additional tests that will be selected, the identifying, the ranking the set of repairs, the determining the possible tests, the ranking the possible tests and selecting further tests until the set includes only one repair and then reporting this repair. Capturing the fault code, preferably, includes capturing an associated set of standard observations corresponding to a subset of observable symptoms, the standard observations selected from a standard observations list and capturing any available test outcomes. Preferably, ranking the repairs further uses an assessment of experience with a set of symptoms, corresponding to observable symptoms associated with the fault code and any available test outcomes, occurring with each repair of the set of the repairs, whether the available test results indict, acquit, or are silent with respect to each repair, and a cost associated with each repair. Ranking the possible tests, preferably, uses an algorithm to rank the possible tests according to a value of the possible test that is dependent on a reduction in the average cost minus a cost to conduct the possible test. The system preferably further utilizes the user interface for displaying the possible tests, as ranked, to a user or remote user for reviewing and selecting a possible test.